inertia

noun

in·​er·​tia i-ˈnər-shə 

-shē-ə

1

a

: a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force

b

: an analogous property of other physical quantities (such as electricity)

2

: indisposition to motion, exertion, or change : inertness

inertial

i-ˈnər-shəl 

-shē-əl

adjective

inertially

i-ˈnər-sh(ə-)lē 

adverb

Did you know?

Inertia is the inherent property of a body that makes it oppose any force that would cause a change in its motion. A body at rest and a body in motion both oppose forces that might cause acceleration. The inertia of a body can be measured by its mass, which governs its resistance to the action of a force, or by its moment of inertia about a specified axis, which measures its resistance to the action of a torque about the same axis.

Synonyms

• idleness
• indolence
• laziness
• shiftlessness
• sloth

Examples of inertia in a Sentence

He blames governmental inertia for the holdup.

After 10 years in an unsatisfying job she overcame her inertia and went back to school.

Recent Examples on the Web

The business seems to be in a weird state of inertia and denial. —Pamela N. Danziger, Forbes.com, 8 May 2025

Using these, scientists were able to model the moment of inertia and Vesta's interior structure. —Keith Cooper, Space.com, 6 May 2025

Yelena, played by Pugh with a keen awareness of the hollow inertia that fuels despair, wants to retire but agrees to perform one final assignment for a big backstabber with too much power, CIA director Valentina Allegra de Fontaine (Julia Louis-Dreyfus). —Randy Myers, Mercury News, 30 Apr. 2025

His radically inferior Black Panther sequel was rewritten in a scramble following the death of star Chadwick Boseman, and its very existence can be seen both as a testament to corporate inertia and a big, forgivable asterisk on an otherwise stellar CV. —Paul A. Thompson, Pitchfork, 22 Apr. 2025

Word History

Etymology

New Latin, from Latin, lack of skill, from inert-, iners

First Known Use

1713, in the meaning defined at sense 1a

Phrases Containing inertia

• moment of inertia

Kids Definition

inertia

noun

in·​er·​tia in-ˈər-shə 

-shē-ə

1

: a property of matter by which it remains at rest or in unchanging motion unless acted on by some external force

2

: a tendency not to move or change

inertial

-shəl 

adjective

Medical Definition

inertia

noun

in·​er·​tia in-ˈər-shə, -shē-ə 

1

a

: a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force

b

: an analogous property of other physical quantities (as electricity)

2

: lack of activity or movement

—used especially of the uterus in labor when its contractions are weak or irregular